2-(2′-Hydroxy-3′-methoxyphenyl)benzothiazole reacts with copper(II) in an ethanol/water mixture to form an O,S chelate which exhibits the remarkable property of changing the chelation site above a pH of ca. 5.0, to the O,N site. The detailed kinetics of this reaction in an ethanol/water mixture (3:1) at a temperature of 25 °C was investigated using a stopped-flow spectrophotometric technique employing a wavelength of 400 nm. The initial complex, Cu(O,S), is formed via a fast, reversible second-order complex formation step whereupon the formation of the Cu (O,N) follows first order kinetics. The Cu(O,N) complex is, however, unstable towards internal electron exchange and after the reaction is complete, a black polymeric material very slowly precipitates out of solution. Rate and equilibrium constants for the postulated reactions are presented and discussed. 相似文献
A thermal analysis of a series of polylactides (PLA) was carried out based on the number of average molecular mass (Mn), and the nature of isomer (D, L and DL). It is confirmed that the glass transition temperature (Tg) of PLA increased as a function of molecular mass irrespective of isomer type except sample with a high polydispersity index.
The melting temperature (Tm) and enthalpy of crystal fusion (ΔHf) of L-isomer increased as the Mn was increased from 1100 to 27500. The degree of crystallinity (χc%) increased as a function of molecular mass. However no crystallization peak was detected in the lower molecular mass range
(550–1400). The non-isothermal crystallization behavior of the PLA melt was significantly influenced by the cooling rate.
Both D and L isomers exhibited insignificant difference in thermal properties and DL lactides exhibited amorphous behavior at identical molecular masses. Change in microstructure showed significant difference
between two isomers. Analysis of the FTIR spectra of these PLA samples in the range of 1200–1230 cm−1 supported DSC observation on crystallinity. 相似文献
Double protection : Efficient Fmoc‐based solid‐phase synthesis (SPPS) of sulfotyrosine (sY) peptides is achieved by incorporating the sY residue(s) as a dichlorovinyl‐protected (DCV) sulfodiester(s) and using 2‐methylpiperidine for Fmoc removal. After removal of the other protecting groups, the DCV group could be cleaved by mild hydrogenolysis giving the sY peptides in good yield.
Atomic transport properties namely the shear viscosity and diffusion coefficients for NixCo1-x, CoxFe1-x and NixFe1-x liquid transition metal alloys are investigated systematically by employing statistical mechanical theory known as the distribution function method. As required we describe the interionic interaction by a local pseudopotential model that can take into account d-band effect adequately and, the pair correlation function is derived from the Percus-Yevick theory for hard spheres where the effective hard sphere diameter is determined by the LWCA thermodynamic perturbation theory. Results for shear viscosity agree well with the available experimental data for the whole range of concentration. 相似文献
In this paper we develop the necessary conditions of optimality for a class of distributed parameter systems (partial differential equations) determined by operator valued measures and controlled by vector measures. Based on some recent results on existence of optimal controls from the space of vector measures, we develop necessary conditions of optimality for a class of control problems. The main results are the necessary conditions of optimality for problems without state constraints and those with state constraints. Also, a conceptual algorithm along with a brief discussion of its convergence is presented. 相似文献
We consider the Dirichlet problem for a class of strongly nonlinear elliptic equations with degenerate coercivity and data
in divergence form. We show that some lower order terms have regularizing effects on solutions. 相似文献
Two uniformities U and V on a set X are said to be H-equivalent if their corresponding Hausdorff uniformities on the set of all non-empty subsets of X induce the same topology. The uniformity U is said to be H-singular if no distinct uniformity on X is H-equivalent to U. The self-explanatory concepts of H-coarse, H-minimal and H-maximal uniformities are defined similarly.It is well known that not all uniformities are H-singular. We show here that there is a property which obstructs H-singularity: Every H-minimal uniformity has a base of finite-dimensional uniform coverings. Besides, we provide an intrinsic characterization of H-minimal uniformities and show that they are H-coarse. This characterization of H-minimality becomes a criterion for H-singularity for all uniformities that are either complete, uniformly locally precompact or proximally fine (e.g., metrizable ones). Some relevant properties which insure H-singularity are introduced and investigated in some aspect. 相似文献
Many researchers examined the existence of global attractors for various types of first and second order lattice dynamical
systems. Here we prove the existence of a global attractor for a new type of second order lattice dynamical systems in the
Hilbert space l2×l2. For specific choices of the linear operators this system can be regraded as a spatial discretization of a continuous damped
nonlinear Boussinesq equation on ℝm,m≥1.
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Let G = (V, E) be a any simple, undirected graph on n ≥ 3 vertices with the degree sequence . We consider the class of graphs satisfying the condition where , is a positive integer. It is known that is hamiltonian if θ ≤ δ. In this paper,
(i)
we give a necessary and sufficient condition, easy to check, ensuring that is nonhamiltonian and we characterize all the exceptional sub-classes.
(ii)
we prove that is either bipartite or contains cycles of all lengths from 3 to c(G), the length of a longest cycle in G.